Combinations of wrap spring clutch and brake mechanisms have been described, together with some of their advantages. U.S. Pat. Nos. 2,652,134 and 3,186,530 describe mechanically actuated devices. U.S. Pat. No. 3,315,773 combines an electromagnetically actuated wrap spring clutch with a permanently actuated slip clutch or brake. In U.S. Pat. No. 3,966,024 a disc brake and wrap spring clutch act together in decelerating and stopping a rotating device.
The electromagnetically actuated clutch of U.S. Pat. No. 4,664,238 used opposing friction surfaces rather than a wrap spring. A similar electromagnetic actuating system appears in U.S. Pat. No. 4,273,226. The magnetic flux flows in two parallel paths through a first coupling member having an intervening air gap or other nonferromagnetic spacing between the paths, and to a second coupling member which is thereby magnetically drawn to and held in contact with the first member.
A wrap spring clutch mechanism is disclosed by Wahlstedt (U.S. Pat. No. 4,263,995). A wrap spring is caused to wrap down onto input and output hubs by a magnetic flux acting between a control ring and an adjacent shoulder ring affixed to the output hub and forming a section of the flux path. The remaining sections defining the flux path and enclosing the electromagnetic coil are fixed in position, only the two rings being rotatable.